Birds probably fly lower in bad weather because of reduced visibility. Air
is densest close to the ground when the air pressure is high, too, so I
doubt that's the answer. A quick look at the Internet tells me that
scientists haven't figured out yet why insects seem more abundant when
there's low pressure before rain. Might be that the air is more stable so
the bugs don't get as much lift and thus don't get as high as when the air
is unstable, as it is often is during the fine weather after a cold front
passes.

Here's the only thing I could find about it:

http://www.springerlink.com/content/r638377853811471/


Pat Valdata
Elkton

-----Original Message-----
From: Maryland Birds & Birding [mailto:[log in to unmask]] On
Behalf Of Joel Martin
Sent: Tuesday, October 27, 2009 3:29 PM
To: 
Subject: Re: [MDOSPREY] Fwd: [ENTOMO-L] Why do swallows fly low before rain

Among duck hunters it's axiomatic that birds fly lower in bad weather; the
explanation being that, when atmospheric pressure is low, the densest air,
which provides the best support, is near the ground. Makes sense to me.

Joel Martin
Catonsville, MD